timer does not update

i created a custom timer class that counts using system time i made a list from this class so i can run multiple timers and made another list with the value used for the timers to start counting. my problem is that when i try to add extra time it does not work.

an example:

 public List<float> _timeleft = new List<float>();
 public List<DeathTimer> _timers = new List<DeathTimer>();

 public void Start()
 {
     _timeleft.Add(5f);
     _timeleft.Add(1f);
     _timeleft.Add(10f);
     
     _timers.Add(new DeathTimer(_timeleft[0], () => Debug.Log("Timer one finished.")));
     _timers.Add(new DeathTimer(_timeleft[1], () => Debug.Log("Timer two finished.")));
     _timers.Add(new DeathTimer(_timeleft[2], () => Debug.Log("Timer three finished")));

    
 }

 public void Update()
 {
     _timeleft[0] += 5f;

     if (_timers.Count > 0)
     {
         foreach (var timer in _timers.Where(a => !a.Started))
         {
             timer.Start();
         }

         foreach (var timer in _timers.Where(a => a.Finished))
         {
             timer.Dispose();
         }
         _timers.RemoveAll(a => a.Finished);
     }

 }

as you can see im adding 5 second every update to timeleft[0] but still the first deathtimer finishes in 5 seconds even though you can see element 0 getting bigger in the inspector. I hope this makes any sense and someone can help me figure out how i can make the timer last longer.

the code for the custom timer below:

 public class DeathTimer : IDisposable
 {
     public bool Finished = false;
     public bool Started = false;
     public  Timer _timer;
     public DeathTimer(float time, Action actionToBeExecuted)
     {
         _timer = new Timer
         {
             Interval = time * 1000, // in milliseconds
             AutoReset = false
         };
         _timer.Elapsed += (o, args) =>
         {
             actionToBeExecuted();
             Finished = true;
         };
     }
     public void Start()
     {
         Started = true;
         _timer.Start();
     }
     public void Stop()
     {
         _timer.Stop();
     }
     public void Dispose()
     {
         _timer.Dispose();
     }
 }